In variable pitch bladed devices such as aircraft propellers and wind turbines, it is imperative that the blades be phased or maintained at substantially identical pitch angles. One system for actuating large wind turbine blades in a pitch change mode of operation while maintaining uniform pitch phase of the blades, employs a slide block which rotates with, and is longitudinally slidable on the main shaft of the turbine. The slide block is connected by means of a plurality of solid links to the wind turbine blades, mounted on a rotational hub in such manner that the blades are pivotable about their own axes. The block is also connected to a plurality of fixed actuators through a bearing mechanism. When an adjustment in a blade pitch is desired, the actuators rectilinearly move the slide block over the shaft thereby moving the links which in turn pivot the blades, the phasing of the blades being maintained by the mechanical connections of these actuating system components. It will be appreciated that such a prior art system is not only massive and costly but requires that each blade and the mounts therefor be capable of withstanding the entire actuator output in the event of blade jamming or disconnection of the other blade or blades. To withstand such actuator output as well as normal, aerodynamic loading, the blades and their mounts must be rather massive further contributing to the cost and weight of the bladed device.
Various mechanical pitch changing mechanisms have been proposed for aircraft propellers, examples of such mechanisms being found in U.S. Pat. Nos. 1,908,894 to Findley and 3,163,232 to Grindle. In the Findley patent, the propeller blades are phased by connection of the blades to a gear set driven by a single electric motor. Such a gear connection, like the slide block mechanism discussed hereinabove, contributes significantly to the weight of the propeller hub thereby introducing substantial costs into the system. In the Grindle patent, an hydraulic motor powers the blades in a pitch change mode of operation by means of a rotating cam-bevel gear arrangement for phasing the blades. However, such an arrangement may also add substantial weight and complexity to the system.
Furthermore, such prior art pitch changing mechanisms employing mechanical blade phasing generally require the simultaneous feathering of all blades to shut the bladed device down. Accordingly, should one of the blades jam and fail to feather, the feathering of the remaining blades is jeopardized.